Transition joints for connection of AC fluid filled to extruded cables from 33 kV to 400 kV

摘要

In many countries a large proportion of the existing high voltage underground network comprises fluid filled paper or polypropylene paper laminate insulated (FF) cables. The number of manufacturers of this type of land cable has reduced significantly and so in many cases replacement or additional FF cables are not available for maintenance or changes in the network. This paper describes a range of compact transition joints that can be employed to connect FF cables to XLPE (or EPR) insulated cables in the voltage range from 33 kV to 400 kV. These are newly developed designs based however on long established components. At 33 kV for example, the main insulation body is an elastomeric straight joint which is normally used as a straightforward XLPE cable straight joint. With the addition of a small number of special components this joint can become part of a simple to install transition joint. Moving up the voltage range at 66/150 kV both single core oil feed and 3 core joints are available with designs incorporating pre-moulded sleeves and epoxy barriers. To simplify jointing of the XLPE cable into the transition arrangement "plug-in" technology is used. In addition, for 3 core FF cables a splitter box arrangement coupled with three single core non-feed joints (the same as the cores used in the 3 core joint) can be employed, the benefits of this being that the joint bay can be much narrower than for the self contained 3 core joint. At 220/275 kV and 400 kV, the transition joints are based on a combination of traditional FF stop joints with modern dry-type plug-in XLPE cable accessory technology. This results in a reliable product which needs no special oil or gas supplies, is mainly pre-fabricated and tested in the factory and has reduced dimensions allowing for a relatively compact joint bay. All these features are new and do not apply to the simple "back to back" arrangement of oil or gas immersed terminations. The range of joints has been subjected to strict development test programs, including elevated voltage tests to breakdown, before official witnessed type testing has been undertaken. At 33 kV to 150 kV the only official testing required is limited to type testing which is fully described in the paper. At 275 and 400 kV levels, approval testing has included type testing but also extended testing to one year similar to the prequalification test requirements of IEC 62067 and in broad agreement with the Technical Brochure being developed by CIGRE WG B1.24 [3]. The testing programs for the 220/275 kV and 400 kV joints are fully described in the paper. The development of these joints was justified and undertaken based on predicted market requirements. It is anticipated that there will be an increasing need for transition joints for many years to come to ensure continued service of the many networks containing FF cables. At the time of writing this paper, the first set of 220/275 kV transition joints of the type described in the paper have been installed and have entered service. Additionally the availability of these joints at 220/275 kV and 400 kV has opened up the possibility of using them not only for diversions and repairs of faults but also as the interface joint between ac XLPE land and FF submarine cables, the demand for the latter product being expected to continue far into the future.